For many years, refrigeration units, such as air conditioners and heat pumps, have used refrigerants consisting of chlorofluorocarbons (CFC's) as heat transfer media. It has recently been discovered that releasing CFC's into the atmosphere damages the ozone layer. Therefore it is necessary to avoid open air release of CFC's during transfer of refrigerant to and from such equipment. A more detailed description of the use of CFC's as refrigerants is discussed in U.S. patent application Ser. No. 478,814, now U.S. Pat. No. 5,020,331 which application is hereby incorporated by reference in its entirety.
U.S. Pat. No. 4,766,733 discloses one type of refrigerant reclamation and charging unit which, rather than using a pump or an auxiliary refrigerant system, utilizes a compressor and condenser and a portion of the refrigerant being evacuated to continuously cool itself. In the reclamation mode, the refrigerant flows in the direction of a standard refrigerant receiver or container by means of a pressure differential created by the cooling.
U.S. Pat. No. 4,363,222 discloses another system and method for withdrawing and charging refrigerant from or into a refrigeration system. Withdrawn refrigerant passes through a vaporizing coil to prevent liquid refrigerant from entering the positive displacement transfer pump. Refrigerant vapor from the pump outlet is liquefied in a cooling coil/heat exchanger, which is, in turn, in communication with a refrigerant disposal storage container.
U.S. Pat. No. 4,938,031 discloses another refrigerant recovery and purification system which consists of an evaporator, a compressor and a condenser, mounted on a two-wheel hand truck. Refrigerant is passed through the evaporator, compressed by the compressor, reliquified at the condenser and fed to a storage container.
U.S. Pat. No. 3,232,070 discloses a device for pumping refrigerant from a refrigeration system. The device comprises a compressor, a condenser, and a drier/strainer mounted on a hand movable, two-wheel cart. Refrigerant is withdrawn from the refrigeration system by the compressor until the refrigerant pressure within the system decreases below atmospheric pressure when the device is cut off. If pressure within the system rebuilds, the device is again activated until the system pressure again drops below atmospheric pressure. The patent further teaches keeping a small amount of refrigerant in the device between uses to keep out moisture and air.
None of the above-discussed refrigerant transfer units enables refrigerant to be efficiently pumped in liquid form or simultaneously in both liquid and vapor forms. Consequently, transfer rates are low, a pound or two per minute at an absolute maximum and typically less. None of the above-described, prior art transfer units are capable of essentially complete evacuation in order to prevent contamination between different types of refrigerants during subsequent transfers. Industry standards currently call for no more than about one-half of one percent contaminating (dissimilar) refrigerant(s). The addition of even small amounts of dissimilar refrigerants into the refrigerant of a relatively large industrial or commercial refrigeration system is not likely to contaminate the system refrigerant sufficiently to drop it below industry standards. However, since the direction of the industry is towards reconditioning and recycling of refrigerant, contamination will become cumulative. Generally speaking, mixed refrigerants cannot be separated economically and returned to industry standard levels for reuse. When finally contaminated, such mixed refrigerants will have to be safely disposed of, also typically at a significant cost.